The present invention is directed to a motion picture projection system capable of detecting a digital soundtrack coded in fluorescent material on the surface of motion picture film.
As is fully described in copending application entitled "Motion Picture Film Having Digitally Coded Soundtrack and Method for Production Thereof", Ser. No. 088,465, filed Oct. 26, 1979, of Custer and Bird, a motion picture soudtrack may be digitally coded with compounds which are colorless and transparent to visible light and which fluoresce in the visible spectrum when exposed to ultraviolet light. Because these fluorescent compounds will not interfere with the visual images on the film the soundtrack may be imprinted over the visible image portion of the motion picture film.
It is known to use various light systems, e.g., the system shown in U.S. Pat. No. 1,928,329 to Oswald, et al. and U.S. Pat. Nos. 3,508,015 and 3,522,388 to Miller. However, these systems apparently do not recognize the possiblity of recording both sound and images on the same area of the film. The patent to Oswald, et al. uses black and white film and visible light through a lens to provide the sound system while the patents to Miller utilize light emitting diodes of varying types. The systems thus suffer from the same deficiency of good sound reproduction as is encountered in the magnetic strip or variable area analog optical type of motion picture sound recording.
U.S. Pat. No. 2,244,733 to Schwarz discloses a sound recording apparatus utilizing ultraviolet light to image a film. Ultraviolet light reflected from the surface of the film is directed to a fluorescent screen to visually monitor the modulation of the mirror galvanometer during the recording operation. In an alternate embodiment, the surface of the film may be uniformly coated with a fluorescent material for the purpose of focusing or checking the modulation on the film (column 2, lines 19-28).
U.S. Pat. No. 2,678,254 to Schneck discusses digital coding and photodiode arrays generally.
Further, the art sometimes accomplishes multiple sound source effects by using separate, but synchronously run, film strips or magnetic tapes. These systems present serious technical problems such as maintaining sound and image synchronization between the two separately run systems, especially when the strip or tape of one of the two systems has a section removed because of repair or for other reasons. This film may be of the standard 16 mm, 35 mm or 70 mm size. In the present invention and use, a plurality of digital soundtracks imaged in a transparent, substantially colorless material which can be excited to fluorescence by ultraviolet light are superimposed over the actual image area. One ultraviolet soundtrack exciter source serves to energize, or cause to fluoresce, all of the soundtracks.
Because of the limited quality of optical and magnetic analog soundtracks in standard use the motion picture industry has been unable to effectively reproduce the detailed realism, presence and aural excitement achieved with high fidelity systems at home and at discotheques and concerts. The accuracy of sound reproduction accepted as standard on records and tapes cannot physically be contained in the analog optical track standardized 50 years ago in cramped and grainy space alongside Edison's inch-wide picture. Within this decade, given digital recording, the art of high fidelity sound reproduction will improve still further, putting the film industry in worse jeopardy of failing to provide sound of equal fidelity.
Digital coding enables complete digital sound handling, including mixing and editing, usually done on magnetic tapes, without tape hiss or noise or degradation of the sound signal accumulating through successive generations of re-recording. With the sound signal reduced to plus/minus ("yes"/"no") bits and with parity check bits to monitor the entry of errors, the identity of successive reproductions can be assured. Thus, the present invention is further directed to a film having a digitally coded soundtrack(s) which records sound as binary number data and reconstructs it with absolute precision.
The archaic analog soundtrack is a "picture" of the wave nature of sound and the detail of the analog sound information must inevitably be mixed together with the intrinsic defects of the recording medium. The distortion which is characteristic of the analog recording means and the noise imposed by the coarse silver grains of the film become inseparable from the desired high fidelity sound.
The essential difference in the digital sound record is that the integrity of the sound information exists separate and immune from the physical nature of the recording medium. It is the intent of fluorescent soundtracking to record a plurality of channels of digital sound across the photographic image space of film as transparent and colorless fluorescent digital words. In digital sound recording, the amplitude of the sound wave is "sampled", or measured, at discrete intervals at a clocked constant repetition rate, as, for example, 50,000 samples per second to record frequencies of up to 20,000 Hz. Each sample is next converted to, for example, 16 bit digital words with one or more parity check bits. The 16 bits of each word used to record the wave amplitude of the sample (the dynamic range) can write any integer between 0 and 65,535. This is considerably more information than can be derived from the compressed amplitude spike of the present standard optical analog soundtrack record that is submerged among silver grains. Following Nyquist's theorem there must be more than two samples taken for each cycle of the highest frequency to be reproduced. Thus, 50,000 samples/sec. (more than 40,000 samples/sec.) can reproduce 20,000 Hz sound.